This invention relates to radar testing apparatus in general and, more particularly, to apparatus for testing range capability and elevation target positioning in tracking radars.
Terrain-following radar is a specialized type of forward looking radar which provides a display of terrain ahead of a low flying military aircraft to permit manual or automatic control in order to maintain a constant altitude above the ground. This radar is comprised of complicated electronics and antenna elements usually located in the nose of the aircraft, such as with the AN/APQ-99 radar system of the RF-4C aircraft. As with any complex system, equipment malfunction and breakdowns do occur. Heretofore it has been the practice to appraise the operation of such a radar system using an AN/APM-395 Tester. This device automatically trouble-shoots, calibrates and initallizes the various components in the system but, unfortunately, requires in excess of eight hours to completely check out the radar. Additionally, the unit is large and cumbersome and requires two people to operate it. Quite often, an aircraft reports a radar malfunction along with a requirement that it be repaired within a certain time period which is substantially less than eight hours. In this situation, the only recourse is to perform trial-and-error component substitution relying on experienced technicians with day-to-day troubleshooting experience. Clearly, a need exits for some sort of text equipment to provide a quick reaction repair time capability with a reasonable degree of confidence that the basic functions of range accuracy and target elevation are operating properly.
An additional need exits with respect to the AN/APM-395 Tester. This testing device performs testing on the radar's target positioning circuits to observe its operation when presented with a target, such as a mountain. The AN/APM-395 performs this test by simulating a target which is infinitely high with respect to elevation and checking for a corresponding reaction of the radar's pitch steering bar. Clearly, it would be better to simulate a target with a definite altitude when checking the operation of the pitch steering bar.
Prior work in this area includes U.S. Pat. No. 2,876,447 which discloses an apparatus for monitoring a radar system by producing a visual indication when transmitter power and receiver sensitivity are within predetermined limits. Also, U.S. Pat. No. 4,053,890 teaches a radar testing apparatus in which a simulated target echo is automatically varied in range and signal strength and injected into a radar receiver to determine range sensitivity. While each of these patents is suitable for its intended purpose, neither invention is adaptable for use with the terrain-following radar onboard the RF-4C aircraft.